1. Field of the Invention
The invention relates to the field of high-power broadcasting transmitters.
In particular, it relates to a method for monitoring and controlling an antenna selector, where
the antenna selector has the form of a radio-frequency distribution matrix;
the elements of this matrix are formed by switching points;
the rows of this matrix are associated with a corresponding number of transmitters; and
the columns of this matrix are associated with corresponding number of antennas; and
at the switching points circuit breakers are arranged in each case with the aid of which connections between the transmitters and the antennas can be optionally switched.
The invention also relates to an antenna selector for carrying out the method which exhibits the features enumerated above.
2. Discussion of Background
In a shortwave broadcast transmitting center, the signals of m different transmitters (typically: m=3 . . . 10) are to be switched in accordance with the requirements of the program schedule and the propagation conditions, which fluctuate with the time of the day and season, to the antenna systems which are suitable in each case, that is n different antennas being available (typically: n=5 . . . 100).
Basically, it must be possible to connect each of the m transmitters to each of the n antennas. The group of change-over switches needed for this forms an (m.times.n) matrix having m rows and n columns which is known as antenna selector matrix, for example from the printed document Brown Boveri Information 5/6 (1983), pages 244-247.
The elements of this matrix are formed by switching points which, as a rule, contain two radio frequency rated circuit breakers by means of which, depending on breaker position, the row and column lines from transmitter to antenna, intersecting at the point, are diagonally connected or are switched through in a straight line, each line by itself. Circuit breakers suitable for this purpose (with appropriate microswitches for monitoring) are known, for example, from German Offenlegungsschrift No. 1776 367.
Since the antennas generally only cover a part of the shortwave range, switching operations outside the specified frequency range are not permissible. Therefore, a suitable antenna selector control system must not only sense the positions of the individual circuit breakers and compare them with the predetermined nominal arrangement, but also release or block the selected link between the transmitters and antennas on the basis of a table of permitted frequencies and of the frequency report by the transmitter concerned.
This test must take place continuously even during the operation of the transmitting center since it is possible to change the frequency of a transmitter without changing antenna. In addition, the circuit breakers are in most cases equipped for manual actuation for emergency operation. Due to these facts, a control system must therefore continuously sense and check the breaker position (positions) of the circuit breakers.
For monitoring purposes, the circuit breakers of the radio frequency distribution or antenna selector matrix are then simulated by leading or trailing microswitches which represent a monitoring matrix corresponding to the radio frequency distribution matrix.
In order to monitor the switched connections between the m transmitters and the n antennas, the switch positions of the microswitches in the monitoring matrix have previously been individually sensed in the prior art. With two possible positions per switch and two switches per switching point and with a matrix having m rows and n columns these are (4.times.m.times.n) separate signals for the entire matrix which have to be transmitted in each case via separate signal lines from the site of the radio frequency distribution matrix to the command or control center.
It can be immediately seen that, with the large number of signal lines, this cabling requires a correspondingly great expenditure especially since it is necessary to filter interfering radio frequency from the sensed signals when they enter into the control system.
In the same manner, a large effort is involved when the breaker motors for the circuit breakers are also driven individually and directly, that is to say via (m.times.n) control lines (analogously to the sensing of the breaker position).